If two meshing spur gears are perfectly coplanar and free from manufacturing defects, the entrainment of the driven gear by the driving gear will not subject either shaft to flexural stresses. Such perfection, however, is not realizable in practice; thus, even minor irregularities in the tooth profile will give rise to unbalanced forces resulting at least in objectionable noise, especially during high-speed operation.
It has been proposed to remedy this drawback by an elastic mounting of either or both shafts, thereby facilitating a lateral yielding of the corresponding gears in the presence of stresses due to structural irregularities. Such attempts, however, have not been very successful and give rise to additional problems, particularly where large torques are to be transmitted by these shafts.